I think a grading system is necessary, as well as minor bells and whistles that make dotLRN look nice (e.g. the photo solution Oscar mentioned).
I'd assume a compley survey is fairly high on the list of priorities, though I have no clue what people would like to see there.
Stability and performance is important to a certain degree (if you manage to run it with 40k users, that should be sufficient for most educational institutions).
Internationalization for sure (as we are heavily marketing it, we should adhere to our promises there).
